1. Field of the Invention
This invention generally relates to an ink transfer arrangement for and method of transferring ink to an engraved die surface of a reciprocating die in a printing press and, more particularly, in an intaglio die stamping and embossing press for producing engraved stationery.
2. Description of the Prior Art
Intaglio printing on paper from an engraved line is thought to have originated in the fifteenth century. Typically, a fifteenth century artist would hand engrave a portrait on a plate and, after applying ink over the engraved plate, the portrait was printed by means of a manually operated plate press.
It was not until the turn of the twentieth century that motor driven die stamping and embossing presses of the type disclosed in U.S. Pat. Nos. 558,860; 695,542 and 842,865 were developed. These presses included an ink fountain for containing a supply of ink, a die having an engraved surface, an ink transfer arrangement for transferring ink from the ink supply to the engraved die surface, and a vertically reciprocatable press ram for pressing sheet material such as paper against the inked die surface to produce engraved stationery. At the time, and for many years later, the paper to be printed was hand fed to the printing press, typically at maximum speeds of about 1500 to 2500 impressions per hour. The advent of automatic paper feeders increased maximum printing speeds to about 2500 to 4000 impressions per hour. Sometime around 1940, thermography, also called raised printing, made serious inroads into the production and sale of genuine engraved stationery. The maximum printing speeds at which letterpress or offset presses could be run was much faster than that of the die stamping presses. Some examples of offset presses are disclosed in U.S. Pat. Nos. 2,546,793; 2,737,109; 2,788,742; 3,347,160; 3,412,677; 3,505,952; 3,611,924; 3,701,316 and 3,934,508. A color inking attachment for a printing press is shown in U.S. Pat. No. 2,096,385.
All of the aforementioned die stamping presses from their beginning and, indeed, up to the present time, have used similar ink transfer arrangements to transfer the ink from the ink supply in the ink fountain to the engraved die surface of the die prior to pressing by the press ram. Typically, for example in U.S. Pat. No. 842,865, a cylindrical inking roller is connected at its opposite ends to the ends of a pair of transfer arms about 8" to 10" long. The transfer arms carry the inking roller and pivot in a large arc, typically greater than 30.degree.. When the transfer arms carry the inking roller upwardly, the inking roller picks up ink from a main cylindrical fountain roller that is partially immersed in the ink fountain. When the transfer arms carry the inking roller downwardly, the ink-laden inking roller deposits and distributes its ink over the engraved die surface. The arcuate distance traveled is about 8" to 10" upwardly and downwardly, depending on the press in question.
There are numerous disadvantages to the aforementioned prior art ink transfer arrangement. Primarily, the maximum printing speed at which the die stamping press can be operated is limited by the time taken to ink the die by the inking roller. The longer the distance through which the inking roller moves, the slower is the maximum printing speed. Faster printing speeds were a primary consideration in the development of thermography.
When the speed of the transfer arms is increased beyond a certain point, ink is thrown off from the inking roller all over the adjacent parts of the press. In most cases, depending on the viscosity of the ink, the upper speed limit of the printing process is in the neighborhood of 4500 impressions per hour. A very large percentage of the ink in current use is water-based ink which has a relatively low viscosity, thereby worsening the ink-throwing problem.
In addition, because of the relatively long time interval involved in moving the inking roller from the die to the ink fountain and back, the portion of the printing cycle during which the inking roller is in inking engagement with the fountain roller is very small. Hence, the fountain roller must be rotated at excessive speeds so that it can completely cover and distribute ink over the entire outer circumferential surface of the inking roller during that small portion of the printing cycle. However, the fountain roller is subject to overheating at higher speed, with concomitant vaporization of the ink. The higher printing speeds also result in larger magnitude vibrations which, in turn, have been found to develop undesirable harmonics, causing the transfer arms and the inking roller carried thereon to act in an uncontrollable fashion.
Other problems with known die stamping presses involved such difficulties as cleaning the ink transfer arrangement, replacing the components thereof and adjusting the positions of the components thereof. The fountain roller was typically virtually permanently mounted on the fountain, and it was difficult and time consuming to replace the fountain roller. The position of the inking roller relative to the fountain roller was typically not readily adjustable except by laborious procedures. When an auxiliary fountain roller was used in conjunction with the main fountain roller to meter superfluous ink from the latter and thereby control the thickness of the ink layer thereon, it was typically very painstaking to finely adjust the position of the auxiliary roller. Periodic cleaning of the ink transfer arrangement was typically lengthy in duration. In the event that any of the aforementioned rollers had to be removed from their normal operating positions and replaced and/or cleaned, then extensive readjustment of the various components was necessary, thereby leading to long periods of down time, with concomitant high overhead and labor costs.